FAQ: Why doesn't the projection defined in ArcCatalog change the projection of data in ArcMap?

Question

Why doesn't the projection defined in ArcCatalog change the projection of data in ArcMap?

Answer

Defining a projection in ArcCatalog for your data simply adds projection information to your data that can be used by ArcGIS. Defining a projection does not transform the coordinates of your data, and therefore your data will not appear differently in ArcMap.

Defining a projection for your data is however a very important step when working with data in ArcGIS. By defining a projection, you enable ArcMap to properly overlay your data with other data, perhaps in a different projection. Defining a projection for your data also allows you to project your data to any other projection on the fly in ArcMap.

Note:For shapefile and coverage data, projection information is stored in a .prj file, a text file that is stored with the data. For Geodatabase data, this information is stored internal to the geodatabase.

Note:You can also define a projection for your data using ArcToolbox's Define Projection Wizard.

Note:If you want to transform the coordinate geometry of your data to a different coordinate system (reproject your data), use ArcToolbox's Project Wizard.